This invention relates to milling devices used for reducing the size of particles of milling good and for uniformly mixing two or more components of milling good.
Two types of prior art milling devices used for producing and mixing fine grained material are the ball mill and the colloid mill.
One problem with the ball mill is the unmilled particles that are trapped in the brim of the lid and the accumulation of unmilled particles, on the vertical wall of the barrel, which results in an extended tail of the distribution function of the grain size toward increasing grain size. The ball mill also has a comparatively large amount of milled products which adhere to the balls, to the barrel and to the lid. This is undesirable when milling small amounts of milling good and makes the cleaning of the mill more difficult. In the ball mill, it is practically impossible to dry-mill sticky powders.
Dry-milling with the colloid mill is not possible. Also, a large amount of high precision work is needed in making a colloid mill and thermal expansion is a problem which makes the apparatus very costly to produce.
There is no known apparatus which will provide screening action for very fine particle sizes.